The human tooth minerals are impure non-stoichiometric forms of calcium hydroxy apatite, ideally, Ca10(PO4)6(OH)2. The 'impurities' are present as minor constitutents (eg, CO3=, Mg2+) and as trace elements (eg, F-,Sr2+,Li+) and are nebulously associated with the apatite and with dental caries. Except for the well-documented cariostatic effect of ingested and topical F-, the cariogenic/cariostatic properties attributed to many trace elements are conflicting and circumstantial. ---The goal of this research is to define the role of trace elements on the formation (==mineralization/remineralization) and on the chemical stability (==caries resistance/susceptibility) of dental apatites. Based on he qualitative data obtained to date, this study will provide quantitative experimental evidence showing that the effect of F- and of other trace elements on the chemical stability is, to a significant degree, a consequence of their effects on the structural/physical properties (size, morphology, strain/defects, stoichiometry, composition) of the apatite. ---The specific aims are: (1) to determine the effects of a series of cationic and anionic elements on the formation of apatites; (2) to define the manner of association, whether incorporated or surface bound, thus providing insights as to the possible mechanisms by which an effect is manifested; (3) if incorporated, to determine their effects on the structural/physical properties; (4) to determine synergistic effects with F- or CO3=; (5) to determine physico-chemical properties of dental apatites: (a) enamel of known trace element conc; (b) enamel from teeth of known ages, (c) 'white spot' and 'sound' enamel; (d) fluorosed enamel(e) fluoridated and non-fluoridated apatites; (6) to determine effects of dissolution properties when element is a substituent in the apatite and when a component of the solution. ---Studies on dental apatites will be paralleled with studies on synthetic apatites prepared by precipitation or by hydrolysis of CaHPO4/CaHPO4. 2H2O in solutions containing the trace elements in identical conc., pH (5 and 7.5) and temp. (37 and 100C). ---The physico-chemical techniques will include: chemical analyses (atomic absorption), x-ray diffraction, infrared, electron microscopy, thermo-gravimetric anal, dissolution in acetate buffer (pH 5, 37C, exposure times, 10 to 120 min). --The long term goal is to provide quantitative information which will be useful in developing effective formulations of topical and remineralizing agents for preventive dentistry.